1. Field of the Invention
This invention relates to a digital computer for use in controlling the operation of an automotive vehicle internal combustion engine and, more particularly, to a fail-safe system for use with such a digital computer.
2. Description of the Prior Art
In recent years, stored program digital computers have widely been used in various control systems. Such a control system has been found advantageous in the ease with which a variety of sophisticated controls can be handled, but it is subjective to a control program breakage causing a stop of program execution due to disturbances such as external noises when incorporated in an automotive vehicle for controlling the operation of its internal combustion engine.
FIG. 1 is a block diagram showing a typical digital computer contained control system. The control system includes a control unit 4 performing controls in accordance with the program instructions stored in a memory 5. The control unit 4 is normally designed to perform multioperation using interrupt signals which may be generated by interrupt signal generators. Although three interrupt signal generators 1 to 3 are shown in FIG. 1 as generating different types of interrupt signals S.sub.1, S.sub.2 and S.sub.3, respectively, it is to be noted that a desired number of interrupt signal generators may be provided. The control unit 4 may be comprised of a microcomputer which receives interrupt signals S.sub.1, S.sub.2 and S.sub.3 to execute the respective control programs 51, 52 and 53 stored in the memory 5 and receives no interrupt signal to repeatedly execute the control program 54 related to a background job (BGJ).
In order to check execution of the control programs, an attempt may be made to generate a check signal for each program segment, but such an attempt requires a very complex signal processor to handle many interrupts.